Fresh cervical mucus, human or otherwise, is difficult to obtain in large quantities and degrades rapidly once collected from its source. The testing of vaginal pharmaceuticals, drug delivery methods and fertility aids, for example, depend on a readily obtainable, time stable supply of cervical mucus. For this reason, there is a great need for the development of a synthetic mucus formulation with characteristics similar to that of fresh human cervical mucus.
Cervical mucus is produced by the cervical glands in the cervix. Cervical mucus acts as a biological filter, preventing the influx of vaginal bacterial flora and enhancing sperm survival. Cervical mucus is an essential element to conception and its physical properties change predictably and cyclically during the menstrual cycle. It is produced in response to the action of the hormones estrogen and progesterone. During the first half of the cycle, before mid-cycle ovulation, as estrogenic hormone release increases, the cervical mucus produced is watery, copious, clear and stretchy. After ovulation, the quality of the mucus changes in response to increased levels of progesterone becoming thicker, sticker and reduced in amount as the cycle ends.
Mid-cycle cervical mucus represents the best opportunity for the successful introduction of sperm, pharmaceuticals, and similar applications designed to penetrate the uterine system due to a decrease in mucus viscoelasticity. The composition of mid-cycle cervical mucus contains about 1% to 1.5% electrolytes, about 0.5% to 1.0% proteins, about 0.5% to 1.0% lipids, about 0.5% to 5% glycoproteins, and about 95% water. The characteristics of mid-cycle cervical mucus include a pH of about 7.4 and a viscosity of about 2,840 to 10,000 cP.
Mucins are a family of glycoproteins with particularly high molecular weight. Mucins are secreted or expressed by goblet and nongoblet epithelial cells at many body surfaces, including the eyes, pancreatic ducts, gallbladder, prostate and mainly, respiratory, gastrointestinal and female reproductive tracts. Mucins are capable of forming viscous and highly hydrated gels, such as mucus, and thereby act as lubricants or protecants in cavities of the body or on body surfaces. At least nine distinct mucin genes have been identified in the human body: MUC1, 2, 3, 4, MUC5AC, MUC5B, MUC6, 7 and 8.
Previous to the present invention, mucus substitutes known in the art included hen egg white, guar gum, hyaluronic acid, acrylimide and polyacrilimide, albumin tyrode solution, and gum tragacanth. Most of the aforementioned substitutes are used only for sperm penetration testing. This limitation in use results because each previously known substitute lacks a glycoprotein fraction representative of fresh cervical mucus.
A synthetic cervical mucus can be used to test the performance of existing and new vaginal product formulations such as fertility drugs, contraceptives and drugs for the treatment of vaginal infections, as well as for other purposes.
Prior patents provide no teaching concerning the use of combinations of viscosity increasing agents and glycoproteins as effective in creating a gel formulation with viscosity, spinnbarkeit, and pH properties comparable to that reported for human cervical mucus.
It is well known in the art that viscosity increasing agents are especially useful in forming gels when crosslinking agents are used to assist in forming gels at low concentrations of viscosity increasing agents and to form gels having properties not obtainable by their use alone. A well known crosslinking agent for viscosity increasing agents, specifically for use with guar gum, is the borate ion which acts as a crosslinking agent with a hydrated viscosity increasing agents to form cohesive structural gels.